The remote Windows host has an application installed that is affected by an integer overflow.
The WinSCP program installed on the remote host is a version prior to 5.1.6. It therefore contains code from PuTTY that is affected by an integer overflow related to handling RSA signature data. This error allows a remote attacker to crash the application.
Upgrade to WinSCP version 5.1.6 / 5.2.2 beta or later.